A typical data storage system includes one or more data storage disks coaxially mounted on a hub of a spindle motor. The spindle motor rotates the disks at speeds typically on the order of several thousand revolutions-per-minute (RPM). Digital information, representative of various types of data, is typically written to and read from the data storage disks by one or more transducers, or read/write heads, which are mounted to a rotatably mounted actuator and pass over the surface of the rapidly spinning data storage disks.
The actuator typically includes a plurality of outwardly extending actuator arms, with one or more read/write transducer assemblies being mounted resiliently or rigidly on the extreme end of the actuator arms. The actuator arms are interleaved into and out of the stack of rotating disks, typically by means of a coil assembly mounted to the actuator. The coil assembly generally interacts with a permanent magnet structure, and the application of current to the coil assembly in one polarity causes the actuator arms and transducers to shift in one direction, while current of the opposite polarity causes the actuator arms and transducers to shift in an opposite direction.
In a typical digital data storage system, digital data is stored in the form of magnetic transitions on a series of concentric, closely spaced tracks comprising the surface of the magnetizable rigid data storage disks. The tracks are generally divided into a plurality of sectors, with each sector comprising a number of information fields. One of the information fields is typically designated for storing data, while other fields contain sector identification and synchronization information, for example. Data is transferred to, and retrieved from, specified track and sector locations by the actuator arms and transducers being shifted from track to track, typically under the control of a controller. The transducer assembly typically includes a read element and a write element.
Writing data to a data storage disk generally involves passing a current through the write element of the transducer assembly to produce magnetic lines of flux which magnetize a specific location of the disk surface. Reading data from a specified disk location is typically accomplished by the read element of the transducer assembly sensing the magnetic field or flux lines emanating from the magnetized locations of the disk. As the read element moves over the rotating disk surface, the interaction between the read element and the magnetized locations on the disk surface result in electrical pulses being induced in the read element, thereby indicating transitions in the magnetic field.
It is common practice to employ a clamping apparatus to securely clamp together one or more data storage disks to the hub of a spindle motor. It can be readily appreciated that a data storage disk must be securely mounted to the spindle motor hub to prevent undesirable slippage between the data storage disk and the clamp apparatus which restrains the disk securely around the hub. Even a minimal amount of slippage between the disk contact surface and clamp contact surface can, for example, result in read/write errors, track misregistration errors, and mechanical fatigue of the spindle motor and data storage disk. A typical clamp apparatus, as illustrated in FIG. 3, includes one or more spacers 63 disposed between adjacently stacked data storage disks 24, with the disks 24 and spacers 63 being forced together and secured around the circular hub 27 of the spindle motor 26 by a disk clamp 61. The disks 24 are generally subjected to appreciable levels of axial or radial forces, or a combination of axial and radial forces, resulting from the clamping force produced by the disk clamp 61. Generally, some degree of bowing, rippling, or other detrimental distortion of the disk 24 surface often results from a non-uniform or non-symmetrical distribution of the forces imparted to the disks 24 or from subjecting the disks 24 to excessively high levels of clamping force.
Many disk clamp apparatus have been disclosed, such as those discussed in U.S. Pat. Nos. 5,274,517 and 5,267,106, which purport to provide effective clamping of a plurality of vertically aligned disks 24 to the hub 27 of a spindle motor 26, while minimizing disk distortion or detrimental curvature resulting from axial and radial loading forces imparted on the disks 24 by the disk clamp 61. The disk distortion produced from excessive loading forces exerted on the disks 24 is particularly pronounced near the inner diameter of the disk 24, and gradually reduces in magnitude at outer diameter locations on the disk 24. If the induced disk distortion is sufficiently pronounced, deleterious contact between the transducer 35 and the distorted disk surface can occur, generally causing damage to both the transducer 35 and the affected area of the disk surface. Even in the absence of disk 24 and transducer 35 contact, the disk distortion may introduce read/write errors, track misregistration errors, and other performance errors of varying severity.
Other disclosed prior art disk clamping schemes employ elastomeric material pressed between the disk clamp 61 contact surface 60 and the contact surface 25 of the data storage disk 24. It is purported that utilizing elastomeric material in this configuration distributes more uniformly the loading forces produced by the disk clamp 61 in a direction extending radially outward from the circumference of the central aperture of the disk 24. Although it is believed that the use of elastomeric material in this manner has yet to be incorporated into a data storage system available in the marketplace, use of such elastomeric materials would likely achieve little success, stemming primarily from the mechanical and thermal instability of the relatively low durometer material, and the perceived necessity to routinely replace the material during the service life of the data storage system.
In a conventional disk clamping apparatus, the clamping force is typically increased in an attempt to further reduce the possibility of disk-to-clamp and disk-to-spacer slippage, thereby increasing the axial loading force on the data storage disk stack. As such, traditional clamping approaches generally rely primarily on static friction between the disk and clamp mating surfaces in order to reduce the possibility of disk-to-clamp and disk-to-spacer slippage. Referring to FIG. 4, there is shown an exaggerated illustration of the contact surfaces 60 and 25 of the disk clamp 61 and data storage disk 24, respectively, in accordance with a prior art clamping apparatus. Although macroscopically the contact surfaces 60 and 25 may appear substantially smooth, at a microscopic level, as depicted in FIG. 4, the topographic irregularities of the two contact surfaces 60 and 25 provide for some degree of static friction between the disk clamp 61 and data storage disk 24 contact surfaces. In order to enhance the advantages afforded by static friction between the disk and clamp contact surfaces 25 and 60 respectively, this contact interface generally comprises a significant percentage of disk 24 surface area surrounding the central aperture of the disk 24. Any increase in the size of the contact interface between the disk 24 and disk clamp 61, however, has the adverse effect of reducing the available data storing surface area of the disk 24. This concomitant reduction in the data storage capacity of the disk 24 significantly effects the storage capacity of a data storage system, and, in particular, small and very small form factor data storage systems.
In the data storage system manufacturing community, there exists a need to increase the data storing surface area of a data storage disk, and to reduce the amount of disk surface area allocated for mounting the disk to the hub of the spindle motor. There exists a further need to substantially reduce or eliminate detrimental disk distortion resulting from clamping forces produced by a clamp apparatus when securely mounting the disk to the spindle motor hub. The present invention fulfills these and other needs.